STUDY ON EASILY SUSPENDED-DEPOSIT ENVIRONMENTS IN AN URBAN RIVER

Abstract

One of non-point sources in the watershed of urban rivers is a river-bed deposit which may easily suspend as a river-flow velocity increases, referred to here as an easily suspended deposit (ESD). To evaluate ESD environments in an urban river, we conducted field measurements in Oohori River with a new device which can easily measure a pick-up rate of the ESD under various flow conditions. The observed data shows that the temporal and spatial variations of the ESD environments are caused due to hydrologic events and changes of flow rate from North-Chiba water conveyance channel. When the pick-up rate P_k is modeled as a power law dependence on bottom stress τ_b, P_k=ατ_bη, the measured results suggest that the coefficients, α and η, also vary appreciablyin time and space.